972. The particles of the chyle and lymph, on mingling with the blood, are scattered through the mass, and become invisible, being apparently lost among the innumerable red corpuscles; but it is not probable that the chyle is immediately converted into blood. If the coagulation of the blood be retarded by the addition of a small portion of the carbonate of potass, the red particles gradually sink some lines below the level of the fluid; and the supernatent liquid is whitish, evidently from the chylous globules mingled with the blood. In ordinary coagulation, the chyle globules are included among the immense number of the red particles of the coagulum, and are thus indistinguishable; but there is reason to believe that the chyle is not converted into blood under at least from ten to twelve hours; it is certain, that in that space of time after the completion of digestion, the serum of the blood is frequently seen to be milk-white, from the quantity of unassimilated chyle still contained in it. 973. How the red colour of the blood is obtained, and whence the capsules of the red particles are derived, if these bodies really possess an external envelop, is wholly unknown. But it has been shown (953 and 955) that in incubation the blood is formed from the substance of the fluid yolk, without the action of any special organ; that at the period when the blood is first generated, no such organs as appear to influence the production of the blood in the adult are in existence; it is, therefore, reasonable to infer that the formation of blood in the adult may not be so dependent on the action of special organs as is commonly supposed; and that the formation of blood from chyle, of blood corpuscles from chyle corpuscles, may take place at all periods of life under the influence of the same general vital conditions as it does in the incubated egg. 974. What change the matter of the blood undergoes by respiration, whether it acquire something without which it is incapable of maintaining life, or part with something the presence of which is incompatible with life, is equally unknown. We only know that the blood, during respiration, changes its colour; but of the nature of the change produced upon its substance we are wholly ignorant. In the present state of our knowledge, the ultimate fact is, that without the change wrought upon the blood by respiration, the blood is incapable of maintaining life; in fact, no proper nutrient fluid is formed.